The present invention relates to the purification of compressed air discharge condensate containing water, oil, dirt and scale. Typically such condensates include a high percentage of water having emulsified and suspended oil therein, a small percentage of separate oil and varying amounts of dirt, scale and the like.
The suspension and emulsification of oil and water found in compressed air system condensate is more severe than in other typical oil contaminated water cases, such as oil spills, industrial processes and general oil-water mixtures. The reason for this are primarily due to the compressed air system itself. In all air compressors oil is directly or indirectly mixed with air being compressed, and the oil is therefore subjected to the intense action of the compression process. The large amount of heat generated by compression and the inherent shearing action cause the oil to vaporize or break down into extremely small particles. Oil, therefore, leaves the compressor as a vapor, mist or droplet and is carried along with the water vapor and liquid also produced by compression in the air stream.
Because of condensation and turbulence, the oil and water are mixed throughout the system thereby creating finely emulsified and suspended oil-water condensate. This oil and water condensate is further mixed when removed from the air system through drain valves which let down both the condensate and compressed air from system to atmospheric pressure. Previous problems are often compounded by the use of compressor lubricants that easily emulsify or contain detergent additives.
Currently a large percentage of compressed air users discard compressed air discharge condensate directly into sewers and storm drains even though there are laws and regulations prohibiting this practice. Many state environmental health organizations are becoming increasingly more active in monitoring and enforcing all regulations governing oil concentrations in waste water. Hence, many compressed air users are obligated to process their condensate on-site or collect it and use off-site processing facilities which can be very expensive.
Prior art oil-water separation equipment and methods are voluminous. Most pertain to oil spills, off shore clean up, shipping and oil field applications where the specific gravity difference between the oil and water is 0.09 or greater. Few are intended for the purification of compressed air system condensate where the specific gravity difference may be lower than 0.01.
Currently the system discharge is subjected to various processes such as gravity separation, coagulating chemicals, ultra-filtration, parallel plate coalescers, carbon adsorption, absorbing media, surface skimmers etc. However, these methods of separation do not effectively purify condensate and they are incapable of dealing with all the various constituents of the condensate. For example, gravity separators, parallel plate coalescers, absorbing media and surface skimmers cannot remove emulsified and suspended oil in water (which can be a large percentage of the oil in a condensate). Coagulating chemicals, ultra-filtration and carbon adsorption cannot deal with gross oil and heavy particulates in the process water.
Other factors also make purifiers impractical, such as size requirements, flow capacities, processing costs and large amounts of human intervention. There are also special requirements of compressed air system condensate purifiers such as being able to handle the large amount of compressed air which is discharged along with the condensate and material compatibility with synthetic compressor lubricants.